Since the 1970s, powder coatings have been a focus of development. In recent years, the use of powder coatings has grown rapidly worldwide due to its environmental friendly nature and tremendous improvement in resins, additives, and equipment technologies.
A glycidyl methacrylate (GMA) based powder coating is a powder coating system often selected for use from among other powder coating systems such as polyester, epoxy, and hybrids thereof, etc. The GMA based powder coatings have been used for 30 years since the first application patent published in 1973 (U.S. Pat. No. 3,752,870). The GMA powder coating has a general reputation for good smoothness, crystal clarity, chemical resistance, high gloss, and excellent outdoor durability. In fact, up to date the GMA powder coating is the only powder coating system selected for automotive full-body clear topcoat applications. GMA powder coatings have also been widely used in aluminum wheel coating, outdoor furniture, garden equipment, light fixtures, and certain industrial applications where extended weatherability is required.
Although GMA powder coatings have been used in many high performance applications, as described above, an improvement in the powder coating appearance and acid etch resistance is needed to meet current higher automotive standards. One manner most people have selected to improve powder coating appearance is to reduce the powder coating resin melt viscosity from existing systems. However, by doing that, the resin glass transition temperature was also reduced and the powder coating resins and final formulated powder suffered physical storage stability. Using refrigerated shipping and storage became a common practice in some high performance GMA powder coating applications. The refrigerated shipping and storage increase the cost for these applications.
Furthermore, to attempt to improve final coating properties such as mar and chemical resistances, many people increased the contents of the functional monomer, GMA, in GMA powder coating resin compositions. However, the increase of GMA functional monomer contents in resin compositions typically results in the increase of secondary hydroxyl groups generated during final curing of the powder coatings, as shown in the following GMA powder coating curing reaction scheme:

The secondary hydroxyl groups generated during the GMA powder coating curing reaction increased the hydrophilic characteristics in a final coating which typically reduced the GMA powder coating's humidity resistance, acid etch resistance, and filiform corrosion resistance. In the typical practice of GMA powder coatings, the higher weight % GMA monomer-containing resins give less acid etch resistance. Although the above secondary hydroxyl group could be further reacted with some other secondary curing mechanism, most of them are not efficient due to the hindering from the first highly cross-linked network.
Therefore, there is a high demand to provide a novel GMA powder coating resin with high cross-linking density without reducing the acid etch or other corrosion resistance. Embodiments of this disclosure provide novel GMA powder coating resin compositions which give a good GMA powder coating, good melt flow, and give a final coating with excellent smoothness, chemical resistance, and mar resistance with improved acid etch resistance. Further, it is anticipated that embodiments of this disclosure will provide improved corrosion resistance, such as filiform corrosion.